Architect Richard Williams expanded and renovated his wife Kim's childhood home in Chevy Chase, Maryland, modernizing and enlarging it without disturbing the midcentury neighborhood.

When Kim Williams was growing up in Chevy Chase, Maryland, as Kim Prothro, her large family (of seven children) lived in a house on a wooded double lot that was connected to a smaller prefab structure by a 16-foot breezeway. As children left home, her parents, who still live in the original home, rented the prefab. "We used to call it 'the other house," says Kim, who is now an architectural historian working in historic preservation in nearby Washington, D.C. These days, however, Kim and her husband, architect Richard Williams, call that revamped structure "our house."

Kim and Richard had been living in a circa-1901 apartment in the capital district, but as their family began to grow—first came Katie, then Jamie—they went looking for larger digs. "If I'd had the opportunity to buy a beautiful Federal-style house and renovate it," says Kim, "I would've been happy, but what you could get for your money, from an architect's perspective, wasn't worth it. Richard had also reached a point in his career where he wanted something modern for himself, and I was actually a little covetous of some of the projects he'd built for clients." So they bought the prefab "other house" and moved in with her parents while they decided what to do with it.

"I don't think it was supposed to last very long," says Richard of the structure, which had single-glazed windows and "leaked like a sieve." At first they contemplated demolishing and rebuilding. The decision not to do so sprang partly from building-code issues, but also from Kim's preservationist tendencies and Richard's architectural concern about site specificity.

The couple had always liked the quiet neighborhood's midcentury-modern character. "These were interesting homes built in the 1940s and '50s," observes Richard. So they resolved to keep the shell of the structure and add on, doubling living space to about 4,000 square feet. But, he says of the renovation, "the language, scale and massing is still very appropriate to this leafy, low-density setting."

"The beauty of the place was the way it formed an L and opened out to a patio overlooking the woods," adds Kim. "I wanted a lot of light, circulation between inside and outside and lots of cross ventilation—I hate air-conditioning." Her husband achieved these qualities by ingeniously alternating steel-framed French doors and clear windows with translucent polycarbonate panels throughout. The latter look like "millions of strands of vermicelli" compressed together, Richard explains. "They do amazing things to light but also have a great material quality."

What the Pros Know"My initial reaction to it was pure visual lust," says architect Richard Williams of the polycarbonate panels he used throughout the house. He discovered, however, that the "tight cell" technology of CPI Daylighting's product (most polycarbonate is "wide cell," with more space between the honeycomb cells of its structure) also had other advantages. "It does amazing things to bend, refract and confuse light," he explains. These effects and a molecularly bonded surface coating provide, according to the company (CPIDaylighting.com), 97 percent UV-ray reduction, which also mitigates yellowing of the material (Williams notes that "it has a 35-year shelf life"). "The honeycombs have thermal-insulating qualities," he continues, and the tightness of the cells also "gives weight and density to a product that is usually flimsy. So it's quite impact-resistant; it won't shatter or break, and it has a hail warranty. I've had tree limbs fall on the roof panels without making a ding." It's 100 percent recyclable, easily cut and drilled through, and doesn't require messy or toxic caulk or sealants. The panels simply "zip together with an aluminum batten element," Williams says, adding that they've never leaked.

Wherever there was "an unfortunate view" (another house, for example), Richard deployed polycarbonate panels to obscure it yet still allow the passage of light. Their most dramatic use is above the kitchen and master bath, on a section of roof that interrupts the standing-seam copper that shields the interior spaces. "It brings bright light into the middle of the house," says Richard. "It's very green in that respect, because we rarely use artificial lighting. Stepping into the bathroom is like entering a courtyard. And at night the roof glows like a lantern. Basically we used the roof panels like a light fixture."

Richard worried that light levels under the polycarbonate panels would be too bright relative to the rest of the house. "I was afraid people would go snow blind," he jokes. His remedy? A perforated plywood ceiling suspended in the kitchen that disperses light more judiciously and also maintains the continuity of the ceiling plane, something the resident architect felt would unify old and new spaces more harmoniously. "We inherited eight-foot ceilings in the old house," he says, so they modulated ceiling heights where desired by excavating rather than raising the roof. "Wherever there are 12-foot ceilings, it's the result of stepping down 4 feet."

In the master bedroom, Richard angled the ceiling upward toward an enormous transom window that he set on a five-foot-high wall, naturally leading the eye to a view of trees and sky. "You're totally connected to nature," he observes, "but you have complete privacy." As for decor, "the stuff from our 1901 apartment didn't work here," he concedes. He asked a friend, a local dealer in midcentury modern named Robin Rose, to help supplement their own furnishings with pieces by Hans Wegner, Jens Risom and Poul Henningsen.

Richard's adaptation of his wife's family compound was "a great preservationist approach," Kim believes. "Even though it's a very modern house, it's contextual. The houses in the neighborhood fit on this hilly terrain in a good way, low on the land. It's a totally different space, yet the surroundings are identical to what I loved about the place when I was a child."

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